Edgeguarding High:
Back Air: This move takes people by surprise a lot. It's best used when the opponent is just trying to drift back on stage. A RAR Bair is decently fast, and has a lot of kill potential. You can also run the same direction they are falling, then jump backwards and Bair. This move is extremely potent when edgeguarding, so always keep it in mind.
Bullet Climax: A charged BC knocks the opponent a good distance away, and can even snipe an opponent recovering high at high enough percents. You can keep firing it after the charged shots have disappeared to create a wall that the opponent is forced to air dodge through, which leaves them open to being gimped down below.
Edgeguarding Sideways:
Down Smash: DSmash is primarily useful for interrupting telegraphed horizontal recoveries, such as Ike's or Ganondorf's Side B. This move is extremely good at getting low to mid percent gimps, as it always spikes-it has no sourspot! This is the move that your opponent should fear when off-stage. If they aren't using a move, make sure to wait for their inevitable air dodge of panic before releasing it.
Neutral Air: Nair is good for knocking opponents away from the ledge. Nair BA is especially good as it lasts for basically as long as you want. It's also good for interrupting quick horizontal recoveries, such as Fox's Side B. It's often your best option to edgeguard sideways.
Bullet Climax: A charged BC knocks the opponent a good distance away, and can even snipe an opponent recovering high at high enough percents. You can keep firing it after the charged shots have disappeared to create a wall that the opponent is forced to air dodge through, which leaves them open to being gimped down below.
Edgeguarding Low:
Down Smash: This should only really be used on opponents hanging on the ledge without any invincibility frames, as it nets an easy spike. It can also be used to interrupt an opponent's vertical or horizontal recovery, if it doesn't sweetspot the ledge. Other than that, it doesn't have much use, as the move is still mostly above stage.
Neutral Air: Down below the stage is where Nair really shines. It knocks the opponent at a very difficult angle to recover from, especially if they've burned their double jump. In addition, BA extends the hotbox of the move as long as necessary, while keeping the knickknack roughly the same. It's also good at interrupting recoveries with no hitboxes, such as Pit's or Rosalina's Up B. It's generally best not to FF, since that makes it easier to airdodge through. Nair is definitely one of your most useful moves for edgeguarding low.
Down Air: Dair is great at interrupting all sorts of recoveries, even those with hitboxes. Note that the move only spikes at her heel, so make sure to hit with that. The best way to recover after a Dair is with WT. It's often best to just rapidly press Up + B, even while the Dair is active (this is known as buffering). Finally, make sure to start the Dair above the stage. If you start it too low, you will go too far down and lose a stock before you can WT.